This invention relates to the connection of tubular strut elements to a common node or hub. It has a particularly useful application in lightweight skeletal framework structures. These structures may be used by the National Aeronautics and Space Administration in missions involving the exploitation of space.
Projects presently under consideration include such items as extremely large antenna for communications or earth surveillance, space based manufacturing facilities, and solar power stations for converting and transmitting collected solar energy to earth. These missions are characterized by structures which have large areas even by earth standards. The prospect of orbiting such structures provides unparalleled challenges for developing extremely efficient structural concepts. The success of these missions will also depend on the success of the structural designer in developing new and unique ways to fabricate and assemble large structures.
Although the Space Shuttle represents an improvement in orbital payload capability, it is also limited to an anticipated payload of sixty-five thousand pounds and a cargo bay fifteen feet in diameter and sixty feet in length. Realistically, any mission involving large structures or technology development in space in the near future must be accomplished via Space Shuttle. It is therefore advantageous to develop efficient structural concepts to minimize the total mass which must be orbited and for maximum utilization of the cargo bay area to permit weight critical payloads for Space Shuttle to be achieved and minimize the total number of flights required.
One space structure that has been considered appropriate for such missions is a three-dimensional truss network which may be in the kilometer size in two directions. Such a structural truss would be an assemblage of highly efficient compression members such as cylinders or truss columns. These compression members must also be compatible with the Shuttle packaging constraints.
A joint system in such an assemblage must produce a structurally sound joint with no axial play. Furthermore, the in-situ assembly of one of these structures could be accomplished by astronauts working in the restraining environment of outer space. The weightless environment and the restrictions of movement place severe constraints on the astronauts' ability to perform manual tasks. Consequently, the joint system must be designed to be quickly engaged, without complicated mechanical fasteners or welding, and must require a minimum of engagement force.
The assembled structure will consist of hundreds of structural columns, with each column being attached to hub joints on both ends. The stress on individual columns will be exerted in a longitudinal direction, toward the end nodes or joints. As a consequence, the assembly of the structure in space will have to be accomplished using joints which employ transverse or side engagement. The conventional longitudinal manner of making joint connections is not feasible given the operational requirements of these structures.